PRTG Manual: HTTP Content Sensor

The HTTP Content sensor monitors a numerical value returned by a Hypertext Transfer Protocol (HTTP) request. In the returned HTML page, each value must be placed between square brackets [ ]. See the example below.

It shows the returned numbers in dedicated channels, one channel for each value.

Which channels the sensor actually shows might depend on the monitored device and the sensor setup.

This sensor type does not support Secure Remote Password (SRP) ciphers.

Limited to 50 Sensor Channels

PRTG does not officially support more than 50 sensor channels. Depending on the data used with this sensor type, you might exceed the maximum number of supported sensor channels. In this case, PRTG will try to display all sensor channels. However, please be aware that you will experience limited usability and performance.

Add Sensor

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you will not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.

The following settings for this sensor differ in the Add Sensor dialog in comparison to the sensor's Settings tab.

HTTP Specific

Value Type

Define what kind of values your HTML file gives back. Choose between:

Integer: An integer is expected as return value.

Float:A float is expected as return value, with a dot . between pre-decimal position and decimal places. In this setting, the sensor will also display integer values unless they don't produce a buffer overflow.

The sensor cannot handle string values.

Number of Channels

Define how many values your HTML file gives back. The sensor handles each value in its own sensor channel. Each value must be placed between square brackets [ ]. Enter the number of bracket-value pairs that the defined URL will return. Please enter an integer value.

Do not enter a number less than the number of values returned. Otherwise you will get an error message.

Sensor Settings

On the details page of a sensor, click the Settings tab to change its settings.

Usually, a sensor connects to the IP Address or DNS Name of the parent device where you created this sensor. See the Device Settings for details. For some sensor types, you can define the monitoring target explicitly in the sensor settings. See below for details on available settings.

Enter one or more Tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.

There are default tags that are automatically predefined in a sensor's settings when you add a sensor. See section Default Tags below.

You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.

It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with round parentheses (()) or angle brackets (<>).

Priority

Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. Top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).

Default Tags

httpsensor

HTTP Specific

Timeout (Sec.)

Enter a timeout in seconds for the request. If the reply takes longer than this value defines, the sensor will cancel the request and show a corresponding error message. Please enter an integer value. The maximum value is 900 seconds (15 minutes).

Script URL

Enter the URL the sensor connects to. It has to be URL encoded! If you enter an absolute URL, this address will be independent of the IP Address/DNS Name setting of the device this sensor is created on.

PRTG uses a smart URL replacement that allows you to use the parent device's IP Address/DNS Name setting as part of the URL. For more information, see section Smart URL Replacement below.

Value Type

Shows the kind of values that the HTML file returns. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

This sensor type implicitly supports Server Name Identification (SNI), an extension to the TLS protocol.

Advanced Sensor Data

Content Changes

Define what the sensor will do if the content of the monitored web page changes. Choose between:

Ignore changes: No action will be taken on change.

Trigger 'change' notification: The sensor will send an internal message indicating that the web page content has changed. In combination with a Change Trigger, you can use this mechanism to trigger a notification whenever the web page content changes.

Sensor Result

Define what PRTG will do with the sensor results. Choose between:

Discard sensor result: Do not store the sensor result.

Write sensor result to disk (Filename: Result of Sensor [ID].txt): Store the last result received from the sensor to the Logs (Sensors) directory in the PRTG data folder on the probe system the sensor is running on (on the Master node if in a cluster). File names: Result of Sensor [ID].txt and Result of Sensor [ID].Data.txt. This is for debugging purposes. PRTG overwrites these files with each scanning interval. For more information on how to find the folder used for storage, see section Data Storage.

This option is not available when the sensor runs on the Hosted Probe of a PRTG hosted by Paessler instance.

Authentication

Authentication

Define if the web page at the configured URL needs authentication. Choose between:

No authentication needed

Web page needs authentication

User

This field is only visible if you enable Web page needs authentication above. Enter a username. Please enter a string.

Password

This field is only visible if you enable Web page needs authentication above. Enter a password. Please enter a string.

Authentication Method

This field is only visible if you enable Web page needs authentication above. Select the authentication method the given URL is protected with. Choose from:

Basic access authentication (HTTP): Use simple HTTP authentication. This is the default setting and suitable for most cases. This authentication method transmits credentials as plain text.

Windows NT LAN Manager (NTLM): Use the Microsoft NTLM protocol for authentication. This is sometimes used in intranets for single sign-on.

Digest Access Authentication: Use digest access authentication that applies a hash function to the password, which is safer than basic access authentication.

We recommend that you use the default value.

Sensor Display

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel will always be displayed below the sensor's name. The available options depend on what channels are available for this sensor.

You can set another primary channel later by clicking the pin symbol of a channel in the sensor's Overview tab.

Graph Type

Define how different channels will be shown for this sensor.

Show channels independently (default): Show an own graph for each channel.

Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This will generate an easy-to-read graph that visualizes the different components of your total traffic. This option cannot be used in combination with manual Vertical Axis Scaling (available in the Sensor Channel Settings settings).

Stack Unit

This setting is only available if stacked graphs are selected above. Choose a unit from the list. All channels with this unit will be stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Inherited Settings

By default, all following settings are inherited from objects higher in the hierarchy and should be changed there, if necessary. Often, best practice is to change them centrally in the Root group's settings, see section Inheritance of Settings for more information. To change a setting only for this object, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You will then see the options described below.

Select a scanning interval (seconds, minutes, or hours) from the list. The scanning interval determines the time the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.

If a Sensor Query Fails

Define the number of scanning intervals that a sensor has time to reach and check a device again in case a sensor query fails. The sensor can try to re-reach and check a device several times, depending on the option you select here, before it will be set to a Downstatus. This helps you avoid false alarms if the monitored device has only temporary issues. For previous scanning intervals with failed requests, the sensor will show a Warning status. Choose from:

Set sensor to down immediately: The sensor will show an error immediately after the first failed request.

Set sensor to warning for 1 interval, then set to down (recommended): After the first failed request, the sensor will show a warning status. If the following request also fails, the sensor will show an error.

Set sensor to warning for 2 intervals, then set to down: Show an error status only after three consecutively failed requests.

Set sensor to warning for 3 intervals, then set to down: Show an error status only after four consecutively failed requests.

Set sensor to warning for 4 intervals, then set to down: Show an error status only after five consecutively failed requests.

Set sensor to warning for 5 intervals, then set to down: Show an error status only after six consecutively failed requests.

Sensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval until they show an error. It is not possible to set a WMI sensor to Down immediately, so the first option will not apply to these sensor types. All other options can apply.

If a sensor has defined error limits for channels, it will always show a Down status immediately, so no "wait" option will apply.

If a channel uses lookup values, it will always show a Down status immediately, so no "wait" options will apply.

Schedules, Dependencies, and Maintenance Window

Inheritance for schedules, dependencies, and maintenance windows cannot be interrupted. The corresponding settings from the parent objects will always be active. However, you can define additional settings here. They will be active at the same time as the parent objects' settings.

Schedule

Select a schedule from the list. Schedules can be used to monitor for a certain time span (days, hours) every week. With the period list option it is also possible to pause monitoring for a specific time span. You can create new schedules and edit existing ones in the account settings.

Schedules are generally inherited. New schedules will be added to existing ones, so all schedules are active at the same time.

Maintenance Window

Specify if you want to set up a one-time maintenance window. During a maintenance window, the current sensor and all child objects will not be monitored. They will be in a Paused status instead. Choose between:

Not set (monitor continuously): No maintenance window will be set and monitoring will always be active.

Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.

To terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends to a date in the past.

Maintenance Begins

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Maintenance Ends

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Dependency Type

Define a dependency type. You can use dependencies to pause monitoring for an object depending on the status of another object. You can choose from:

Use parent: Use the dependency type of the parent device.

Select a sensor: Use the dependency type of the parent device. Additionally, pause the current sensor if another specific sensor is in a Down status or in a Paused status caused by another dependency. Select below.

Master sensor for parent: Make this sensor the master object for its parent device. The sensor will influence the behavior of its parent device: If the sensor is in a Down status, the device will be paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor will be paused if the parent group is paused by another dependency.

Testing your dependencies is easy! Simply select Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later, all dependent objects should be paused. You can check all dependencies in your PRTG installation by selecting Devices | Dependencies from the main menu bar.

Dependency

This field is only visible if you enable Select a sensor above. Click the Search button and use the object selector to select a sensor on which the current sensor will depend.

Dependency Delay (Sec.)

This field is only visible if you enable Select a sensor above. Define a time span in seconds for dependency delay.

After the master sensor for this dependency comes back to an Up status, monitoring of the dependent objects will be additionally delayed by the defined time span. This can help avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Please enter an integer value.

This setting is not available if you set this sensor to Use parent or to be the Master sensor for parent. In this case, please define delays in the parent Device Settings or in its parent Group Settings.

Define which user group(s) will have access to the object you're editing. A table with user groups and types of access rights is shown. It contains all user groups from your setup. For each user group, you can choose from the following access rights:

Inherited: Use the access rights settings of the parent object.

None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree, though not accessible.

Read: Users in this group can see the object and review its monitoring results.

Write: Users in this group can see the object, review its monitoring results, and edit the object's settings. They cannot edit access rights settings.

Full: Users in this group can see the object, review its monitoring results, edit the object's settings, and edit access rights settings.

You can create new user groups in the System Administration—User Groupssettings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.

The sensor calls the URL with every scanning interval and only regards the two values in square brackets [ ], handling each of them in one sensor channel. The additional description text and HTML tags are not necessary. In this example they are added in case a human calls the URL.

If you define the number of channels as 1, the sensor will read only the first value. The second value will be ignored. Using 3 as number of channels will result in a sensor error message.

Smart URL Replacement

Instead of entering a complete address in the URL field of an HTTP sensor, you can merely enter the protocol followed by a colon and three slashes (that means you can enter either http:/// or https:/// or even a simple slash / as equivalent for http:///). PRTG will fill in the parent device's IP address orDNS name in front of the third slash automatically.

Whether this results in a valid URL or not depends on the IP address or DNS name of the device where this HTTP sensor is created on. In combination with cloning devices, the smart URL replacement makes it easy to create many like devices.

For example, if you create a device with DNS namewww.example.com and you add an HTTP sensor to it, you can provide values in the following ways:

Providing the value https:/// in the URL field, PRTG will automatically create the URL https://www.example.com/

Using the value /help in the URL field, PRTG will automatically create and monitor the URL http://www.example.com/help

It is also possible to provide a port number in the URL field, which will be taken over by the device's DNS name and internally added, for example, http://:8080/

Smart URL replacement does not work for sensors running on the Probe Device.

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